N.I.H. funding for the crossover design randomized clinical trial ""Inhaled Nitric Oxide and Bronchopulmonary Dysplasia"" began on 2/1/98. Study enrollment began in July of 1998. With respect to subject enrollment to date, in the first 19 months, we have enrolled 15 infants in the study: 9 at Children's Hospital of Philadelphia and 6 at The Hospital of the University of Pennsylvania. Randomization and blinding have been successfully carried out according to study protocol. Treatment assignments remain blinded; however 10 of 15 infants enrolled to date have had a significant improvement during one of their study gas periods. They received a prolonged course of treatment with one gas (either nitric oxide or placebo). There have been no adverse events directly attributable to iNO. No infant enrolled in the study has expired during the 10 crossover study period; however, 3 of 15 infants (20%) ultimately expired 15, 18, and 21 days after enrollment. Based on an algorithm developed by Overstreet et al. to estimate mortality risk in 30 day old ventilated preterm infants, the overall predicted probability of mortality for the study infants enrolled to date is 42%. In addition, the recently completed clinical trial of antenatal thyrotropin-releasing hormone for the prevention of chronic lung disease in preterm infants, involving 996 women (NEJM 338:493-8, 1998) described a mortality rate of 33% for preterm infants 24-26 weeks gestation. Details of the clinical courses of the three infants who died are summarized below.